Upstanding, elongate objects such as wooden structural poles, posts, pilings and the like eventually deteriorate structurally after they have been installed in the ground for an interval of time. One particular type of such deterioration, frequently referred to as "groundline rot," is damage to the wooden, elongate object caused by moisture, insects, fungi, or other wood destroying organisms about the point along the pole's length at which it enters the ground, i.e. about the pole's "groundline." The section of the pole thus damaged may extend between one-half to one meter along the pole's length into the ground beneath the pole's groundline and may extend a similar distance along its length upward above its groundline. This groundline rot not only reduces the pole's compressive, load carrying capacity, but also reduces its bending and shear strengths. In addition to the normal deterioration of wooden poles about their groundline as described above which is caused by a pole's exposure to the elements, analogous structural groundline damage may also occur if a pole is struck by a motor vehicle or, in rural areas, if struck by livestock. To prevent catastrophic failure of a weakened pole particularly under stress such as during a storm, maintenance must be performed periodically to ensure the continuing structural soundness of poles.
A most common technique for maintaining the structural integrity of poles is to periodically inspect them for structural damage and then to simply replace excessively weakened ones. If a pole to be replaced supports electrical wires, power lines, for the transmission of electricity, replacing it first requires that electrical power be removed from the power lines so they can be physically disconnected from the top of the pole. Such removal of electrical power from a power line, of course, discontinues electrical service to a utility's customers serviced by that line. Once the power lines have been disconnected from the top of the pole, the pole is then held by some type of grapple or other device while it is cut off near its groundline. After the pole has been severed, its upper portion is removed, the underlying stump dug up, and a new pole reinserted into the same hole from which the stump was removed. The replacement pole must be installed in the same physical location as that occupied by a weakened pole so the power lines may be supported in the same general location when reinstalled at the top of the new pole. Because discontinuing electrical service to a utility's customers results in a revenue loss to the utility and because of the cost for labor and materials involved in replacing a pole, it is readily understood that replacing a pole is expensive.
Because weakened poles frequently remain structurally sound other than for groundline rot or similar groundline damage, it has been recognized for some time that reinforcing poles about their groundline to restore lost strength could obviate the need for their replacement. One rather unsophisticated pole reinforcement technique consists simply in first placing a shorter section of pole or similar structural member into the ground immediately adjacent to the weakened pole. Then the sound upper portion of the weakened pole above its groundline is secured to this immediately adjacent reinforcement. An analogous technique is that taught in U.S. Pat. No. 405,658 issued to M. E. Campany entitled "Pole or Post Protector." The technique taught in that patent consists in driving elongated, semicircular sheet metal braces shaped to fit the outer surface of a pole into the ground immediately adjacent to and on opposite sides of a structurally weakened pole. After these sheet metal braces have been embedded into the ground about the pole, metal straps are then secured about them above the ground to secure the weakened pole between them. A slightly simpler technique employs only a single metal sheet metal brace driven into the ground immediately adjacent to a pole to which the pole is then secured with metal straps. The principal problem with these various pole reinforcement techniques is that they restore a weakened pole's strength principally along a plane passing through the longitudinal axes of the pole and of its reinforcement while providing significantly less reinforcement in directions perpendicular to that plane.
Rather than attempting to reinforce a weakened pole, one pole repair technique, identified commercially as ModPole.TM., replaces the in-ground and weakened above-ground portions of a pole with a precast concrete pole base replacement. To install this precast concrete pole base replacement, again the pole must first be held by some type of grapple or other device while it is cut off above the groundline damage. After the pole has been thus severed, the grapple is then used to hold the pole to one side while the in-ground portion of the pole is pulled out of the ground together with the weakened portion. The hole remaining after the in-ground portion has been thus extracted is then cleaned out with an auger and the precast concrete pole base replacement inserted therein. With the pole base replacement thus installed in the ground, the base of the pole's upper portion, which has been held to one side by the grapple after being severed from the lower portion, is then inserted into a hollow, cylindrically shaped socket provided on the upper end of the precast concrete pole base replacement. The socket provided on the upper end of the pole base replacement is fabricated with a significantly larger diameter than that of the pole which it receives so that a hollow annulus is established between the outer surface of the pole's base and the inner surface of the socket. Thus, after the pole's base has been inserted into the socket it is secured there by filling this hollow annulus with a grouting material.
One significant disadvantage of repairing a pole with the ModPole technique, is that the pole must be supported and moved while the precast concrete pole base replacement is installed. Consequently, this technique for repairing a weakened pole may require removing the power lines from and reinstalling them at the top of the pole analogous to performing a complete pole replacement. Even if physical disconnection of the power lines from the top of a pole is unnecessary, the movement of the pole and the possibility of an accident are sufficiently great that discontinuing power transmission is necessary while a pole is repaired. Thus, the lost revenue from discontinued electrical service plus the possible expense of disconnecting and reconnecting the power lines at the top of the pole make ModPole base replacement comparatively expensive. A further difficulty associated with performing a pole repair using the ModPole technique is transporting the relatively heavy precast concrete pole base replacement from the site at which it is fabricated to the pole repair site. Lastly, the relative mass of the ModPole's heavy precast concrete pole base replacement in comparison with a conventional wooden pole significantly increases a utility company's exposure to liability for personal injury if a repaired pole is struck by a motor vehicle.
Yet another pole reinforcement technique is described in a presently pending Patent Cooperation Treaty International Application No. PCT/US84/00043 entitled "Techniques for Establishing Inground Support Footings and for Strengthening and Stabilizing the Soil at Inground Locations" filed by Frank R. Kinnan on Jan. 16, 1984 which claimed the priority date of U.S. patent application Ser. No. 458,817 filed by Frank R. Kinnan on Jan. 18, 1983 which is presently assigned to the Electrical Power Research Institute of Palo Alto, Calif. The technique described in that patent application, which is sometimes referred to as "stubbing," reinforces the weakened section of a pole by surrounding it with a unitary, outer, hollow metal casing. This casing is fabricated with a diameter slightly larger than that of the weakened pole so a hollow annulus is established between the casing and the pole. As with the ModPole base replacement, this hollow annulus is filled with a grouting material and sand to complete the pole reinforcement. As described in that patent application, installing this reinforcing structure about a weakened pole again first requires holding it with some type of grapple or other device while it is cut off near its groundline similar to complete pole replacement or ModPole base replacement. After the pole has been thus severed, similar to ModPole base replacement the grapple is then used to hold the pole to one side while the casing is driven partially into the ground around the pole's remaining stump by a rotary casing driving apparatus secured about the casing's upper edge. With the casing in place, the upper portion of the pole, which has been held to one side by the grapple while the casing was driven into the ground, is then inserted into the open end of the casing projecting upward out of the ground and mated with the stump from which it was severed. Once the upper portion of the pole has been mated with the stump, the hollow annulus between the outer casing and the pole is filled with the grouting material and sand.
While the structural characteristics of this stubbing technique are such that the strength of a reinforced pole is as great as that of a new one, it shares one of the ModPole's disadvantages in that the pole must be supported, cut off, and moved while the reinforcing casing is installed. Thus, simply the lost revenue from discontinued electrical service plus the possible expense of disconnecting and reconnecting the power lines at the top of the pole make the total cost of pole stubbing substantially similar to those for outright pole replacement. Further, because the upper extent of a pole also deteriorates although at a slower rate than at the groundline, the usable service life of a pole reinforced by stubbing is less than that of a new pole. Hence pole stubbing does not offer a significantly attractive cost savings to utility companies in comparison with total pole replacement.
A simpler and markedly more cost effective pole reinforcement technique than stubbing is described in a presently pending Patent Cooperation Treaty International Application No. PCT/US83/01878 entitled "Method and Apparatus for Installing an In-Ground Support Footing Around an Upstanding Elongate Object" filed by Frank R. Kinnan on Dec. 1, 1983 which is assigned to the assignee of the present application. The technique described in that patent application is similar to stubbing except that the metal casing driven into the ground around a weakened pole is assembled from two identical, complementary half-cylinders and is therefore frequently referred to as a "split casing." As taught in that patent application, such a split casing is assembled about a weakened utility pole and driven into the ground about the pole without need for cutting it off, disturbing it, disconnecting the power lines at the top of the pole, or even discontinuing power transmission over the line.
The particular apparatus described in that patent application for driving the split casing into the ground about a weakened pole is a vehicle mounted casing driver unit having a pair of movable jaws hinged together at one end and openable at the other. Thus after the two halves of a split casing have been assembled about a weakened pole, the jaws on this casing driver unit are opened, positioned about the assembled casing, and then closed to surround the casing with their inner surface securely engaging it. This innermost portion of the casing driver's jaws which engage the casing are adapted to rotate about an axis substantially collinear with that of the assembled casing and are further adapted to engage the casing's uppermost edge. Thus, once the casing driver's jaws have closed about the casing and their innermost portion engage it, power may be applied to the casing driver unit to rotate the casing about its longitudinal axis and to apply a force to the casing urging it downward into the ground about the weakened pole. Once this split casing is installed about the pole, the hollow annulus between the casing and the pole is filled with the grouting material and sand thus completing the pole's reinforcement.
All of the prior pole repair techniques described above require using heavy equipment of the type most frequently used in the construction industry. Thus, this equipment such as the casing driver unit described above is well suited to installing split casings about weakened poles only in locations which may be easily reached by the vehicle on which it is mounted. However, in certain urban areas, utility poles are installed along the property line which separates two adjoining lots of land facing onto parallel streets ("lot line poles"). While, in principle, lot line poles could be repaired using vehicle mounted equipment, some persons occupying the land over which such vehicles must pass to reach a pole are certain to resist that use of their land. Further, if structures such as fences or buildings block ready access to a lot line pole, the cost of clearing an access way prior to performing a pole repair and restoring the land to its prior state after a pole has been restored would, in many instances, be so great as to make pole repair economically impractical. Analogously, certain utility poles in rural areas are installed in terrain in which they are virtually impossible to reach with a vehicle. Thus, in general, all the pole repair techniques described above are unsuitable for repairing lot line poles and particular rural poles because of the heavy equipment which they require for performing a pole repair.